1. The Field of the Invention
The present invention relates generally to high speed data transmission systems. More particularly, embodiments of the invention relate to optical micro-modules for use in optical transmitters and passive optical signal propagation devices.
2. The Relevant Technology
The use of fiber optic technology is an increasingly important method of data transmission. Through fiber optics, digital data in the form of light signals is formed by light emitting diodes or lasers and then propagated through a fiber optic cable. Such light signals allow for high data transmission rates and high bandwidth capabilities. Other advantages of using light signals for data transmission include their resistance to electromagnetic radiation that interferes with electrical signals; fiber optic cables' ability to prevent light signals from escaping, as can occur electrical signals in wire-based systems; and light signals' ability to be transmitted over great distances without the signal loss typically associated with electrical signals on copper wire.
Many fiber optic components are capable of splitting, redirecting, relaying, multiplexing, demultiplexing, or otherwise manipulating light signals without the need for electrical input. Such optical components are typically referred to as passive devices in that they do not require a source of energy for their operation. Common examples include optical fibers, lenses, and filters.
However, it is often necessary to connect an electrical signal to a light signal and vice versa. One conventional device used to translate electrical signals into light signals is a transmitter optical subassembly (TOSA). TOSAs typically include an electrical interface for receiving electrical signals; a data encoder/modulator for converting the electrical signals into FM, AM, or digital optical signals, and a light emitting diode or laser to form the light signal. After the light signal leaves the light emitting diode or laser it typically passes through one or more isolators and lenses used to couple the light signal with an optical waveguide, such as a fiber optic cable. Each of the light emitter, isolator(s), and lens(es) are typically structurally distinct and isolated within a TOSA housing.
Similarly, receiver optical subassemblies are used to translate optical signals into electrical signals. One such device is a receiver optical subassembly (ROSA). A typical ROSA may comprise, for example, an optical fiber receptacle and an avalanche photodiode (APD), which operates with a reverse-bias voltage that causes the primary photocurrent to undergo amplification by cumulative multiplication of charge carriers. Typically, the light exiting an optical fiber in the optical fiber receptacle is so divergent that it needs to be collimated or otherwise focused onto the photodiode.
Because of the small size of the various components in optical devices, such as TOSAs, ROSAs, and passive optical devices that couple light signals into optical fibers, and the importance of precisely aligning the components, the optical devices can be relatively difficult and expensive to manufacture. For example, one important passive component typically used to passively couple light signals into an optical fiber is an aspherical glass lens. These aspherical molded glass lenses focus or collimate the light received from a light source, for example a laser diode. These glass lenses typically have an aspheric surface on each side and must be carefully aligned at the proper focal length from the light source and from the optical fiber during the manufacture of the optical device. As a result, both because of their individual cost and the added cost in manufacturing optical devices, glass aspheric lenses add a considerable cost to optical devices.
Accordingly, there is a continuing need for less expensive and more easily assembled and aligned passive devices for use in optical devices to propagate and otherwise manipulate optical signals.